def adsb_get_alt(msg):
"""
:param msg: bit string of extended squitter for DF17
:returns: tuple of integers (qbit, altitude), altitude is in feet;
altitude may be None if msg is invalid
"""
qbit = btoi(msg[47])
if qbit:
# [20:26][27:33] (bits M and Q removed)
altstr = msg[40:47] + msg[48:52]
alt = btoi(altstr) * 25 - 1000
else:
# Swap bits around, see Annex 10, 3.1.1.7.12.2.3
# Squitter bit order:
# C1 A1 C2 A2 C4 A4 [no-M] B1 Q B2 D2 B4 D4
# 40 41 42 43 44 45 46 47 48 49 50 51
# Transponder bit order:
# D2 D4 A1 A2 A4 B1 B2 B4 C1 C2 C4
altstr = msg[49]+msg[51] + msg[41]+msg[43]+msg[45] + \
msg[46]+msg[48]+msg[50] + msg[40]+msg[42]+msg[44]
try:
alt = glie.xpdr.code_to_alt(altstr)
except ValueError:
return (0, None)
return (qbit, alt)
def adsb_get_alt(msg):
"""
:param msg: bit string of extended squitter for DF17
:returns: tuple of integers (qbit, altitude), altitude is in feet;
altitude may be None if msg is invalid
"""
qbit = btoi(msg[47])
if qbit:
# [20:26][27:33] (bits M and Q removed)
altstr = msg[40:47]+msg[48:52]
alt = btoi(altstr) * 25 - 1000
else:
# Swap bits around, see Annex 10, 3.1.1.7.12.2.3
# Squitter bit order:
# C1 A1 C2 A2 C4 A4 [no-M] B1 Q B2 D2 B4 D4
# 40 41 42 43 44 45 46 47 48 49 50 51
# Transponder bit order:
# D2 D4 A1 A2 A4 B1 B2 B4 C1 C2 C4
altstr = msg[49]+msg[51] + msg[41]+msg[43]+msg[45] + \
msg[46]+msg[48]+msg[50] + msg[40]+msg[42]+msg[44]
try:
alt = glie.xpdr.code_to_alt(altstr)
except ValueError:
return (0, None)
return (qbit, alt)
def cpr_decode_lat(oddstr, cprstr, ourlat):
"""
:param oddstr: odd/even flag as 1-char bitstr
:param cprstr: the CPR of target latitude
:param ourlat: the latitude of the station in float degrees
:returns: the target latitude in float degrees
"""
Nb = 17 # 17 for airborne, 14 for ground/intent, 12 for TIS-B.
NZ = 15 # Doc 9871 C.2.6.2
if len(cprstr) != Nb:
raise AppError("Latitude bit string size is not 17: %d" % len(cprstr))
if oddstr != '0' and oddstr != '1':
raise AppError("Invalid odd/even: %d" % oddstr)
lat_s = ourlat
i = btoi(oddstr)
# Formulas only use the arc fraction, so convert YZ to fraction right away.
YZf = float(btoi(cprstr)) / (1 << Nb)
# Dlat_i is either 6.0 or 360/59==6.1016949152
Dlat_i = 360.0 / (4.0 * NZ - i)
# Zone index number
j = math.floor(lat_s/Dlat_i) + \
math.floor(0.5 + (lat_s % Dlat_i)/Dlat_i - YZf)
Rlat = Dlat_i * (j + YZf)
return Rlat
def cpr_decode_lat(oddstr, cprstr, ourlat):
"""
:param oddstr: odd/even flag as 1-char bitstr
:param cprstr: the CPR of target latitude
:param ourlat: the latitude of the station in float degrees
:returns: the target latitude in float degrees
"""
Nb = 17 # 17 for airborne, 14 for ground/intent, 12 for TIS-B.
NZ = 15 # Doc 9871 C.2.6.2
if len(cprstr) != Nb:
raise AppError("Latitude bit string size is not 17: %d" %
len(cprstr))
if oddstr != '0' and oddstr != '1':
raise AppError("Invalid odd/even: %d" % oddstr)
lat_s = ourlat
i = btoi(oddstr)
# Formulas only use the arc fraction, so convert YZ to fraction right away.
YZf = float(btoi(cprstr))/(1<<Nb)
# Dlat_i is either 6.0 or 360/59==6.1016949152
Dlat_i = 360.0 / (4.0 * NZ - i)
# Zone index number
j = math.floor(lat_s/Dlat_i) + \
math.floor(0.5 + (lat_s % Dlat_i)/Dlat_i - YZf)
Rlat = Dlat_i * (j + YZf)
return Rlat
def recv_msg_adsb(linestr):
x = linestr.find('*')
if x != 0:
return
x = linestr.find(';')
if x == -1:
print(TAG+": bad message format", file=sys.stderr)
return
msglen = x-1
if msglen != 14 and msglen != 28:
print(TAG+": bad message length", msglen, file=sys.stderr)
return
msg = scatter_bits(linestr[1:x])
df = msg[0:5]
if df == '10001': # DF17
addr = msg[8:32]
c_crc = glie.crc.esq_crc(msg[0:-24])
a_crc = msg[-24:]
if c_crc == a_crc:
crc_status = "OK"
else:
x_crc = glie.crc.xor(addr, c_crc)
if x_crc == a_crc:
crc_status = "aOK"
else:
crc_status = "Error"
ca = msg[5:8]
if ca == '101': # CA5
typ = btoi(msg[32:37])
if 9 <= typ <= 18: # Airborne Position with barometric altitude
qbit, alt = adsb_get_alt(msg)
if alt is None:
alt = -1
lat, lon = adsb_get_pos(msg)
print("addr %x alt (Q=%d) %d lat %f lon %f CRC:%s" % \
(btoi(addr), qbit, alt, lat, lon, crc_status))
# XXX string value, really?
if crc_status == 'OK':
craft.update(addr, (time.time(), alt, lat, lon))
elif typ == 19: # Airborne Velocity
# P3
print(" DF17 CA5 Type 19 CRC:%s" % (crc_status,))
else:
# P3
print(" DF17 CA5 Type", typ, "CRC:%s" % (crc_status,))
else:
# P3
print(" DF17 CA", btoi(ca), "CRC:%s" % (crc_status,))
else:
# P3
print(" DF", df, btoi(df))
def recv_msg_adsb(linestr):
x = linestr.find('*')
if x != 0:
return
x = linestr.find(';')
if x == -1:
print(TAG + ": bad message format", file=sys.stderr)
return
msglen = x - 1
if msglen != 14 and msglen != 28:
print(TAG + ": bad message length", msglen, file=sys.stderr)
return
msg = scatter_bits(linestr[1:x])
df = msg[0:5]
if df == '10001': # DF17
addr = msg[8:32]
c_crc = glie.crc.esq_crc(msg[0:-24])
a_crc = msg[-24:]
if c_crc == a_crc:
crc_status = "OK"
else:
x_crc = glie.crc.xor(addr, c_crc)
if x_crc == a_crc:
crc_status = "aOK"
else:
crc_status = "Error"
ca = msg[5:8]
if ca == '101': # CA5
typ = btoi(msg[32:37])
if 9 <= typ <= 18: # Airborne Position with barometric altitude
qbit, alt = adsb_get_alt(msg)
if alt is None:
alt = -1
lat, lon = adsb_get_pos(msg)
print("addr %x alt (Q=%d) %d lat %f lon %f CRC:%s" % \
(btoi(addr), qbit, alt, lat, lon, crc_status))
# XXX string value, really?
if crc_status == 'OK':
craft.update(addr, (time.time(), alt, lat, lon))
elif typ == 19: # Airborne Velocity
# P3
print(" DF17 CA5 Type 19 CRC:%s" % (crc_status, ))
else:
# P3
print(" DF17 CA5 Type", typ, "CRC:%s" % (crc_status, ))
else:
# P3
print(" DF17 CA", btoi(ca), "CRC:%s" % (crc_status, ))
else:
# P3
print(" DF", df, btoi(df))
def xor(a, b):
length = len(a)
if length != len(b):
raise AppTraceback('xor on unequal length arguments')
step = 20
ret = ""
for i in range(0,length,step):
len1 = min(length - i, step)
ai = btoi(a[i:i+len1])
bi = btoi(b[i:i+len1])
res = ai ^ bi
ret += format(res, "0>%db" % len1)
return ret
def cpr_decode_lon(oddstr, cprstr, tgtlat, ourlon):
Nb = 17 # 17 for airborne, 14 for ground/intent, 12 for TIS-B.
if len(cprstr) != 17:
raise AppError("Longitude bit string size is not 17: %d" % len(cprstr))
if oddstr != '0' and oddstr != '1':
raise AppError("Invalid odd/even: %d" % oddstr)
Rlat = tgtlat
lon_s = ourlon
i = btoi(oddstr)
XZf = float(btoi(cprstr)) / (1 << Nb)
# NL() defined in AppC.2.6.2.d Note 5
nl = NL(Rlat)
if nl - i == 0:
Dlon_i = 360.0
else:
Dlon_i = 360.0 / (nl - i)
m = math.floor(lon_s/Dlon_i) + \
math.floor(0.5 + (lon_s % Dlon_i)/Dlon_i - XZf)
Rlon_i = Dlon_i * (m + XZf)
return Rlon_i
def cpr_decode_lon(oddstr, cprstr, tgtlat, ourlon):
Nb = 17 # 17 for airborne, 14 for ground/intent, 12 for TIS-B.
if len(cprstr) != 17:
raise AppError("Longitude bit string size is not 17: %d" % len(cprstr))
if oddstr != '0' and oddstr != '1':
raise AppError("Invalid odd/even: %d" % oddstr)
Rlat = tgtlat
lon_s = ourlon
i = btoi(oddstr)
XZf = float(btoi(cprstr))/(1<<Nb)
# NL() defined in AppC.2.6.2.d Note 5
nl = NL(Rlat)
if nl - i == 0:
Dlon_i = 360.0
else:
Dlon_i = 360.0/(nl - i)
m = math.floor(lon_s/Dlon_i) + \
math.floor(0.5 + (lon_s % Dlon_i)/Dlon_i - XZf)
Rlon_i = Dlon_i * (m + XZf)
return Rlon_i
